Actuator systems for deflecting optical waveguides, and devices for processing optical signals comprising same

ABSTRACT

Actuator systems ( 10 ) are provided for inducing one or more static deflections, such as bends, in optical waveguides ( 12 ), to alter spectral characteristics of an optical signal transmitted through the waveguide. The actuator systems ( 10 ) can include actuators ( 28 ) that deflect the waveguide ( 12 ), and a controller ( 40 ) that controls the actuators ( 28 ) so that the deflections in the waveguide ( 12 ) are tailored to produce desired spectral characteristics in the optical signal. The actuator systems ( 10 ) can be used in conjunction with, for example, a fused fiber optic coupler ( 12 ) to form a wavelength selective switch. The actuator systems ( 10 ) can be used in conjunction with other types of waveguides to form other types of optical signal processors ( 14 ).

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional application of and claims priority topending non-provisional U.S. patent application Ser. No. 13/751,670filed on Jan. 28, 2013, which is hereby incorporated by reference in itsentirety.

BACKGROUND OF THE INVENTION

Statement of the Technical Field

The inventive arrangements relate generally to devices for processingoptical signals, such as but not limited to wavelength selectiveswitches and filters. More specifically, the inventive arrangementsrelate to actuator systems that induce static deflections, such asbends, in optical waveguides, to alter the spectral characteristics ofoptical signals transmitted through the waveguides.

Description of the Related Art

Providers of fiber-optic networks face a constant demand to increasenetwork capacity. This demand results in a need for increased spectralutilization and dynamic reconfigurability in fiber optic networks.Wavelength division multiplexing, using wavelength selective switchingdevices such as reconfigurable optical add-drop multiplexers (ROADMs),is one commonly-used way to meet these requirements. The losses inoptical power associated with these types of devices, however, arerelatively high, e.g., 6-8 dB. Although optical amplifiers can be usedto compensate for such losses, the use of optical amplifiers canadversely affect the optical signal to noise ratio, which imposes apractical limitation on length and capacities of the optical pathwayswithin the networks.

All-fiber wavelength selective switches have been developed. Theseswitches operate via propagation mode coupling in waveguides such asmultimode or tapered optical fibers, and fused fiber optic couplers. Themode coupling is accomplished by subjecting the waveguide to anacoustically-induced traveling flexural wave.

All-fiber wavelength selective switches, in general, have favorable,i.e., relatively low, power losses. It is difficult to obtain a desiredspectral response in such switches, however, because the amplitude andphase of the traveling flexural wave cannot be controlled within theinteraction region of the waveguide. Moreover, the traveling flexuralwave imparts a frequency shift to the coupled light. This frequencyshift can result in undesirable amplitude modulation of both the throughand switched optical waves.

Optical amplifiers are ubiquitous in modern fiber optic networks. Longhaul dense wavelength division multiplexed (DWDM) networks requireoptical amplifiers with performance (gain and noise figure) that isuniform across a broad wavelength range. This is typically achieved byincorporating spectral equalizing filters within the optical amplifier.These filters provide loss that varies with wavelength to compensate forthe wavelength dependent gain of the amplifier. Typical low lossequalizing filters have a fixed response (they cannot be adjusted afterfabrication). This lack of adjustability is a limitation as thewavelength dependence of an optical amplifier gain typically varies as afunction of the number, power and wavelength of the DWDM channels inputto the amplifier.

Dynamic spectral equalizing filters have been developed but thesedevices rely on the same technologies employed by the previouslydescribed wavelength selective switches and also suffer the samelimitations.

SUMMARY OF THE INVENTION

Actuator systems are provided for inducing one or more staticdeflections, such as bends, in optical waveguides, to alter spectralcharacteristics of an optical signal transmitted through the waveguide.The actuator systems include actuators that deflect the waveguide, and acontroller that controls the actuators so that the deflections in thewaveguide are tailored to produce desired spectral characteristics inthe optical signal. The actuator systems can be used in conjunctionwith, for example, a fused fiber optic coupler to form a wavelengthselective switch. As another example, the actuator systems can be usedwith a single mode fiber, tapered single mode fiber or etched singlemode fiber to form a dynamically reconfigurable spectral equalizingfilter useful in optically amplified fiber optic networks. The actuatorsystems can also be used in conjunction with the aforementioned andother types of waveguides to form other types of signal processingdevices such as band stop and band pass filters.

Systems for processing optical signals comprise an optical waveguide, avoltage source, and a deflector device configured to statically deflectthe waveguide. The deflector device can be, for example, a plurality ofpositioning elements that each include an actuator such as apiezoelectric, thermal, pneumatic, hydraulic, magnetic, or electrostaticactuator. The deflector device is electrically connected to the voltagesource and is responsive to a voltage applied thereto by the voltagesource. The systems also comprise a controller communicatively coupledto the voltage source. The controller is operative to control thevoltage supplied to the deflector devices.

Actuator systems for use with optical waveguides comprise a voltagesource and a plurality of positioning elements. Each of the positioningelements comprises an actuator. The actuator is electrically connectedto the voltage source, and operates to statically deflect the opticalwaveguide in proportion to a voltage provided to the actuator by thevoltage source. The systems also comprise a controller communicativelycoupled to the one or more voltage sources and operating to vary thevoltage provided to each of the actuators to thereby control the staticdeflection of the optical waveguide.

Systems for modifying optical signals include an optical waveguide fortransmitting the optical signal and an actuator system comprising aplurality of positioning elements located proximate the waveguide. Thepositioning elements each have an actuator that operates to cause astatic deflection in the waveguide. The static deflection alters aspectral response of the waveguide.

Methods for altering spectral characteristics of an optical signal beingtransmitted through a waveguide include inducing one or more staticdeflections, such as bends, in the waveguide to, for example, couplepropagation modes in the waveguide. The methods can also includeproviding an actuator system comprising actuators operative to inducethe deflections, and a controller operative to control the actuators sothat the deflections are tailored to produce desired spectralcharacteristics in the optical signal.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will be described with reference to the following drawingfigures, in which like numerals represent like items throughout thefigures and in which:

FIG. 1 is a front view of an optical signal processor, with positioningelements of an actuator system of the optical signal processor in anon-energized, un-deflected state, and depicting an optical waveguide ofthe optical signal processor as a fused coupler for illustrativepurposes only;

FIG. 1A is a side view of a bimorph plate from which a bank ofpositioning elements of the actuator system shown in FIG. 1 is formed;

FIG. 2 is a top view of the optical signal processor shown in FIG. 1,with the positioning elements in a non-energized, un-deflected state;

FIG. 3 is a top view of an optical signal processor shown in FIGS. 1 and2, with the positioning elements in an energized, deflected state;

FIG. 4 is a side view of the optical signal processor shown in FIGS.1-3, with the positioning elements in a non-energized, un-deflectedstate;

FIG. 5 is a block diagram depicting various electrical components of theactuator system of the optical signal processor shown in FIGS. 1-4;

FIG. 5A is a block diagram depicting various electrical and mechanicalcomponents of the optical signal processor shown in FIGS. 1-5;

FIG. 6 is a graphical depiction of the spectral characteristics of anoptical signal that has been processed by an optical signal processorsimilar to the optical signal processor shown in FIGS. 1-5A;

FIG. 7 is a graphical representation of the coupling coefficient betweentwo modes of the waveguide of the optical signal processor referred toin FIG. 6, induced by the actuator system of the optical signalprocessor of FIGS. 1-4, to produce the spectral characteristics depictedin FIG. 6;

FIG. 8 is a perspective view of an alternative embodiment of the opticalsignal processor shown in FIGS. 1-5, with positioning elements of anactuator system of the optical signal processor in a non-energized,un-deflected state;

FIG. 9 is a perspective view of another alternative embodiment of theoptical signal processor shown in FIGS. 1-5, with the positioningelements in a non-energized, un-deflected state;

FIG. 10 is a side view of another alternative embodiment of the opticalsignal processor shown in FIGS. 1-5, with positioning elements of anactuator system of the optical signal processor in a non-energized,un-deflected state;

FIG. 11 is a top view of the optical signal processor shown in FIG. 10,with the positioning elements in the non-energized, un-deflected state;

FIG. 12 is a side view of another alternative embodiment of the opticalsignal processor shown in FIGS. 1-5, with positioning elements of anactuator system of the optical signal processor in a non-energized,un-deflected state;

FIG. 13 is a top view of the optical signal processor shown in FIG. 12,with the positioning elements in the non-energized, un-deflected state;

FIG. 14 is a side view of another alternative embodiment of the opticalsignal processor shown in FIGS. 1-5, with positioning elements of anactuator system of the optical signal processor in a non-energized,un-deflected state;

FIG. 15 is a top view of the optical signal processor shown in FIG. 14,with the positioning elements in the non-energized, un-deflected state;

FIG. 16 is a side view of another alternative embodiment of the opticalsignal processor shown in FIGS. 1-5, with a positioning element of anactuator system of the optical signal processor in a non-energized,un-deflected state;

FIG. 17 is a top view of the optical signal processor shown in FIG. 16,with the positioning element in the non-energized, un-deflected state;

FIG. 18 is a side view of another alternative embodiment of the opticalsignal processor shown in FIGS. 1-5, with positioning elements of anactuator system of the optical signal processor in a non-energized,un-deflected state;

FIG. 19 is a top view of the optical signal processor shown in FIG. 18,with the positioning elements in the non-energized, un-deflected state;

FIG. 20 is a side view of another alternative embodiment of the opticalsignal processor shown in FIGS. 1-5, with positioning elements of anactuator system of the optical signal processor in a non-energized,un-deflected state;

FIG. 21 is a top view of the optical signal processor shown in FIG. 20,with the positioning elements in the non-energized, un-deflected state;

FIG. 22 is a side view of another alternative embodiment of the opticalsignal processor shown in FIGS. 1-5, with positioning elements of anactuator system of the optical signal processor in a non-energized,un-deflected state; and

FIG. 23 is a top view of the optical signal processor shown in FIG. 22,with the positioning elements in the non-energized, un-deflected state.

DETAILED DESCRIPTION

The invention is described with reference to the attached figures. Thefigures are not drawn to scale and they are provided merely toillustrate the instant invention. Several aspects of the invention aredescribed below with reference to example applications for illustration.It should be understood that numerous specific details, relationships,and methods are set forth to provide a full understanding of theinvention. One having ordinary skill in the relevant art, however, willreadily recognize that the invention can be practiced without one ormore of the specific details or with other methods. In other instances,well-known structures or operation are not shown in detail to avoidobscuring the invention. The invention is not limited by the illustratedordering of acts or events, as some acts may occur in different ordersand/or concurrently with other acts or events. Furthermore, not allillustrated acts or events are required to implement a methodology inaccordance with the invention

FIGS. 1-5A depict an actuator system 10. The actuator system 10 is usedin conjunction with an optical waveguide 12 to form an optical signalprocessor 14, shown in FIGS. 1-4. The optical waveguide 12 may assumevarious forms such as: a fused coupler formed from two optical fibersthat have been fused together, as depicted in FIGS. 1-5; a taperedoptical fiber; an etched optical fiber; an multi-mode optical fiber; asingle-mode optical fiber, etc. The optical waveguide is depicted in thefigures as a fused coupler for exemplary purposes only, and thedepiction of the optical waveguide 12 in this manner is not intended toin any way limit the scope of the appended claims.

The actuator system 10 comprises a plurality of deflector devices in theform of positioning elements 20. The positioning elements 20, whenactivated, undergo a displacement in relation to each other, so as toinduce a series of static bends in the optical waveguide 12 as shown inFIG. 3. The respective amplitudes and period of the bends can becontrolled by varying the displacement of the individual positioningelements 20. The bends affect the spectral characteristics of theoptical waveguide 12. For example, the bends can alter the pass band andstop bands of the optical waveguide 12. The spectral characteristics ofthe optical waveguide 12 can thus be controlled by controlling therelative displacements of the positioning elements 20.

The term “static,” as used in the specification and claims to describethe bends and other deflections imposed by the actuator system 10 on theoptical waveguide 12, is intended to denote deflections that aremaintained at a particular location on the waveguide on a steady-statebasis, i.e., for a finite amount of time, as opposed to deflections,such as a traveling flexural wave, that are imposed on a transient orcontinually-varying basis.

The actuator system 10 can include a bank 22 of the positioning elements20, as shown in FIGS. 2-4. The bank 22 can include eight of thepositioning elements 20. The number of positioning elements 20 in thebank 22 is application dependent, and can vary with factors such as thedesired spectral characteristics of the optical signal processor 14, theoverall length of the optical waveguide 12, the period and maximumamplitude of the bends, etc. For example, hundreds or thousands ofpositioning elements can be used to implement single-channel wavelengthselective switching in DWDM transmission systems.

The actuator system 10 can also include a base 23. A lower portion ofthe bank 22 of positioning elements 20 is positioned within, andrestrained by the base 23. The base 23 can be formed from a suitableelectrically-insulative material such as plastic. The base is notdepicted in FIG. 2 or 3, for clarity of illustration.

Each positioning element 20 includes a piezoelectric actuator 29. Thepiezoelectric actuator 29 comprises a metallic inner layer 28, and twolayers 24, 25 of piezoelectric material disposed on opposite sides ofthe inner layer 28 as depicted in FIG. 4. The piezoelectric actuator 29further comprises a metallic outer layer 26 disposed on anoutwardly-facing side of the piezoelectric layer 24, and anothermetallic outer layer 27 disposed on an outwardly-facing side of thepiezoelectric layer 25. The use of a piezoelectric-type actuator isdisclosed for exemplary purposes only. Thermal, pneumatic, hydraulic,magnetic, electrostatic, and other types of actuators can be used inalternative embodiments.

The bank 22 of positioning elements 20 is formed from a piece of bimorphplate 31 comprising a metallic inner layer, and two layers of apiezoelectric material bonded to opposite sides of the metallic innerlayer by a suitable means such as an electrically conductive adhesive orsolder. The piezoelectric layers are oriented so that the polaritiesthereof are aligned. In alternative embodiments, the piezoelectriclayers can be oriented so that the polarities thereof are reversed. Thebimorph plate further comprises two metallic outer layers. Each outerlayer is disposed on an outwardly-facing surface of a respective one ofthe piezoelectric layers. FIG. 1A is a side view of the bimorph plate31, in which one of the outer metallic layers is visible.

The bank 22 is formed by removing portions of the bimorph plate 31. Inparticular, rectangular sections 31 a of the bimorph plate 31 can beremoved at equally-spaced intervals along the length of the bimorphplate 31 as illustrated in FIG. 1A, to form a series of spaced apart,upwardly-extending fingers 31 b that make up the piezoelectric actuators29. The sections 31 a can be removed by a suitable means such as sawing.The metallic inner layer 28 of each actuator 29 is formed by portions ofthe inner metallic layer of the bimorph plate 31 that remain after thesections 31 a have been removed. The piezoelectric layers 24, 25 of eachactuator 29 are formed by remaining portions of the piezoelectric layersof the bimorph plate 31. The metallic outer layers 26, 27 of eachactuator 29 are formed by remaining portions of the metallic outerlayers of the bimorph plate 31.

As shown in FIG. 1A, the sections 31 a removed from the bimorph plate 31do not extend to the bottom of the bimorph plate 31, i.e., the removalof the sections 31 a does not affect the lowermost portion of thebimorph plate 31. Following removal of the sections 31 a, sections 31 cof the outer metallic layers of the bimorph plate 31 are selectivelyremoved by a suitable means such as etching. The sections 31 c arelocated directly below the spaces between the actuators 29 created bythe removal of the section 31 a. The removal of the sections 31 celectrically isolates the metallic outer layers 26, 27 of adjacentactuators 29. (Because the sections 31 a removed from the bimorph plate31 extend over only a portion of the height of the bimorph plate 31, themetallic inner layers 28 of the individual actuators 29 remain inelectrical contact with reach other.)

Each positioning element 20 also includes a contact portion 32. Thecontact portion 32 can be, for example, rigid glass rods that arefixedly coupled to the outer layers 26, 27 of the associatedpiezoelectric actuator 29 by a suitable means such as adhesive. The term“coupled,” as used in the specification and claims, is intended todenote both direct and indirect connections between two or more parts orcomponents.

The optical waveguide 12 is positioned between the contact portions 32of the bank 22, as shown in FIGS. 1-4. As can be seen in FIGS. 2 and 3,the two contact portions 32 of each positioning element 20 are disposedon opposite sides of the optical waveguide 12 and at the axial positionon the waveguide 12. The contact portions 32 contact and bend theoptical waveguide 12 during operation of the actuator system 10, inresponse to deflection of corresponding piezoelectric actuator 29, asshown in FIG. 3.

The use of rigid glass rods as the contact portions 32 of thepositioning elements 20 is disclosed for exemplary purposes only. Rodsand other types of structures, formed from other materials suitable forcontacting the optical waveguide 12, can be used in the alternative.Moreover, the tip of each contact portion 32 can be etched, so as toreduce the contact length and best match the dimensions of the opticalwaveguide 12, in alternative embodiments. In other alternativeembodiments, the positioning elements 20 can be configured without anycontact portions 32, and the piezoelectric actuators 29, and variantsthereof, can be configured to contact directly with the opticalwaveguide 12.

Each contact portion 32 can be formed from a material, such as afluorinated material, having an index of refraction lower than that ofthe optical waveguide 12 to help minimize optical-power losses at theinterface between the contact portion 32 and the optical waveguide 12.Power losses can also be reduced through the use of contact portions 32having low absorption at the desired operating wavelength of the opticalsignal processor.

In applications such as the actuator system 10 where the contactportions 32 are in intermittent contact with the optical waveguide 12,the contact portions 32 should be formed from a material that is softerthan the material from which the optical waveguide 12 is formed, tominimize the potential for wear and other damage to the opticalwaveguide 12 resulting from repeated contact with the contact portions32.

The amplitude of the optical field in certain embodiments of the opticalwaveguide 12 such as a tapered optical fiber or a fused fiber couplercan be relatively high at the outer periphery of the optical waveguide12. Thus, in applications where the actuator system 10 is used inconjunction with an optical waveguide comprising one or more taperedoptical fibers, the contact area between the optical waveguide 12 andthe contact portion 32 of the positioning element 20 can be minimized tohelp reduce optical losses at the interface between the contact portion32 and the optical waveguide 12.

Each piezoelectric actuator 29 is energized by a voltage source 38,depicted in FIGS. 5 and 5A. The metallic outer layers 26, 27 of eachactuator 29 are electrically connected to one side of the voltage source38, and the metallic inner layer 28 of the actuator 29 is electricallyconnected to the other side of the voltage source 38. As discussedbelow, subjecting the actuator 29 to a voltage potential causes theactuator 29 to deflect, which in turn imparts a corresponding deflectionto the portion of the waveguide located proximate the actuator 29. Thedirection of the deflection of the actuator 29 is determined by thepolarity of the voltage source 38 and the magnitude of the deflection isdetermined by the magnitude of the voltage supplied by the voltagesource 38

The voltage source 38 can be, for example, a 300 volt direct-currentpower supply. Other types of voltage sources can be used in thealternative. For example, for piezoelectric and electrostatic actuators,the voltage source 38 may need to supply tens to hundreds of volts andmilliamps of current, while for thermal and magnetic actuators, thevoltage source 38 may only need to provide single-digit voltages andsingle-digit currents. The voltage source 38 is capable of providing avariable, bipolar voltage to each of the positioning elements 20 on anindividual basis. Multiple individual voltage sources, each associatedwith a particular one of the positioning elements 20, can be used in thealternative. The term “voltage source,” as used in the specification andclaims, is intended to denote a single voltage source as well asmultiple individual voltage sources.

The actuator system 10 can also include a controller 40 that iscommunicatively coupled to the voltage source 38 as shown in FIG. 5. Thecontroller 40 can control the voltage level supplied by the voltagesource 38 to the piezoelectric actuator 29 of each positioning element20 on an individual basis.

The controller 40 can include a processor such as a microprocessor 41, amemory 42, and a bus 43, shown in FIG. 5. The bus 43 facilitatesinternal communication between the microprocessor 41 and the memory 42,and external communication with the voltage source 38.

The memory 42 can comprise a main memory 44 and a mass storage device45, each of which is communicatively coupled to the microprocessor 41 byway of the bus 43. The main memory 44 can be, for example, random accessmemory. The mass storage device 45 can be, for example, a hard oroptical disk.

The controller 40 can also include computer-executable instructions 46stored on the memory 43, as shown in FIG. 5. The computer-executableinstructions 46, when executed on the microprocessor 41, cause themicroprocessor 41 to generate control inputs for the voltage source 38.The control inputs cause the voltage source 38 to provide a specificvoltage to one or more of the positioning elements 20, on an individualbasis.

Each positioning element 20, when subjected to a voltage from thevoltage source 38, undergoes a displacement due to the piezoelectricbimorph configuration of the piezoelectric actuators 29. In particular,the outer and inner layers 26, 27 of each piezoelectric actuator 29 actas electrodes when the positioning element 20 is energized. Theresulting electric field causes the piezoelectric layers 24, 25 toundergo a strain along their respective longitudinal axes. Because thelower ends of the piezoelectric layers 24, 25 are restrained, theinduced strain causes the piezoelectric layers 24, 25 to bend, which inturn causes the upper or freestanding end of each piezoelectric layer24, 25 to move substantially to the left or right from the perspectiveof FIG. 4, i.e., in the “+x” or “−x” direction denoted in FIGS. 2-4.Moreover, the alignment of the polarities of the piezoelectric layers24, 25 causes the piezoelectric layers 24, 25 to deflect in the samedirection. The deflection of the piezoelectric layers 24, 25 results ina corresponding deflection in the piezoelectric actuator 29, which inturn drives one of the attached contact portions 32 toward, and intocontact with the optical waveguide 12, as denoted by the arrows 44 inFIG. 3.

Further displacement of the contact portion 32 once the contact portion32 contacts the optical waveguide 12 causes a corresponding localizeddisplacement in the optical waveguide 12, in a direction substantiallyperpendicular to the longitudinal axes of the optical waveguide 12,i.e., in the “+x” or “−x” direction. FIG. 5A is a block diagramdepicting the various components that induce the noted movement in theoptical waveguide 12. FIG. 5A also depicts an optional means foramplifying the displacement of the piezoelectric actuator 29.

The controller 40 can control the operation of the individualpositioning elements 20 so that the positioning elements 20 inducestatic undulations or “microbends” in the optical waveguide 12. Inparticular, the controller 40 can activate or energize the positioningelements 20 so that a positioning element 20 receives a positive voltagethat results in a “+x” displacement. At the same time, the controller 40can energize the positioning elements 20 adjacent to, i.e., to theimmediate left and right from the perspective of FIGS. 2 and 3, of theaforementioned activated positioning element 20 by applying a negativevoltage that results in a “−x” displacement, thereby inducing a bend inthe optical waveguide 12 as shown in FIG. 3.

The direction of the bending or displacement of the positioning elements20 is dependent upon the polarity of the voltage applied thereto. Themagnitude of the bending or displacement is proportional to the voltageapplied thereto. Thus, the direction and magnitude of the individualbends in the optical waveguide 12 can be controlled, via the controller40, by controlling the magnitude and polarity of the voltage supplied toeach positioning element 20 by the voltage source 38. In particular, thestatic microbend at each lengthwise location along the optical waveguide12 can be effectuated by energizing the piezoelectric actuator 29 of thepositioning element 20 associated with that location, and tailoring theapplied voltage to a sign, i.e., polarity, and a level that causes thepiezoelectric actuator 29 to bend so as to produce the desired localizeddeflection in the optical waveguide 12. The computer executableinstructions 46 in the controller 40 can be configured so that thecontroller 40 tailors the voltage level supplied to each of thepositioning elements 20 in such a manner that the positioning elements20 work in conjunction with each other to produce a series of microbendsof the desired period and amplitude in the optical waveguide 12.

The static microbends in the optical waveguide 12 can alter the spectralresponse of the optical waveguide 12 by coupling propagation modes ofthe optical waveguide 12. Coupling between propagation modes can occurwhen the period of the microbend matches the beat length between thepropagation modes being coupled. The beat length L_(B) can be calculatedas follows:L _(B) =λ/|n ₁ −n ₂|Where λ is the wavelength of the optical signal through the opticalwaveguide 12 and |n₁−n₂| equals the absolute value of the differencebetween the effective index of refraction of the propagation modes thatare being coupled. Thus, in order to achieve coupling betweenpropagation modes, adjacent pairs of the contact portions 32 shouldspaced apart in the lengthwise direction of the bank 22 by a distanceless than or equal to one-half of the shortest beat length between thepropagation modes that are being coupled. The period of the microbendformed in the optical waveguide can then take any value greater thantwice the distance between adjacent pairs of contact portions 32 byappropriate selection of the magnitude and polarity of the voltageapplied to the individual positioning elements 20. For example, theoptical wavelength of a wavelength selective switch can thereby beadjusted by altering the period of the microbends formed in the opticalwaveguide.

The ability to couple propagation modes in the optical waveguide 12 canbe used to synthesize a specific desired spectral response in theoptical waveguide 12. For example, FIG. 6 shows the spectral responsethat theoretically can be achieved in an optical signal processor,provided the amplitude of the coupling coefficient between modes can bemade to vary along the length of the coupling region as indicated inFIG. 7.

FIGS. 6 and 7 are excerpted from the following source: Brenne, Skaar,“Design of Grating-Assisted Codirectional Couplers with DiscreteInverse-Scattering Algorithms,” Journal of Lightwave Technology Vol. 21,No. 1, January 2003, in which the authors describe a method forsynthesizing a desired spectral response in an optical coupler byvarying the coupling coefficient between the modes in a prescribed way.FIG. 6 is the resultant spectrum obtained from the coupling coefficientfunction shown in FIG. 7. The amplitude of the coupling coefficientbetween modes is proportional to the magnitude of the deflection of theoptical waveguide 12 (see Birks, et. al. “The Acousto-Optic Effect inSingle-Mode Fiber Tapers and Couplers,” Journal of Lightwave TechnologyVol 14, No. 11, November 1996). It is believed that the couplingcoefficient function shown in FIG. 7 can be produced by an actuatorsystem substantially the same as, or similar to the actuator system 10,provided the actuator system has a sufficient number of positioningelements 20 to introduce the series of arbitrary-amplitude microbendsthat make up the coupling coefficient function. The number ofpositioning elements 20 required to synthesize a particular spectralresponse is related to the fractional bandwidth desired, and the designof the optical waveguide 12.

FIG. 6 demonstrates the characteristics of a relatively flat passband, arelatively high stopband rejection, and relatively low or suppressedside lobes between the passband and stopbands that are desirable in awavelength selective switch for telecom applications, and in other typesof optical signal processors. As discussed above, it is believed thatthese characteristics can be achieved through the use of the actuatorsystem 10 and alternative embodiments thereof. Moreover, because awavelength selective switch or other optical signal processorsconfigured in this manner is an “all-fiber” switch, i.e., the opticalsignal remains within optical fibers throughout the switch, the switchor device produces these desirable spectral characteristics with therelatively low power losses associated with all-fiber switches.

The use of the actuator system 10 in conjunction with an optical signalprocessor 14 configured as a wavelength selective switch comprising afused fiber optic coupler as the optical waveguide 12 is disclosed forexemplary purposes only. The actuator system 10, and variants thereof,can be used to induce static bends and other types of deformations inother types of waveguides to perform other useful functions such as anoptical band-stop filter or dynamic equalizing filter. For example, theactuator system 10 can be used to induce microbends in multi-modeoptical fibers, and in the waist of a tapered optical fiber so as tocouple the modes of the waist. The actuator system 10 can also be usedto induce microbends in single-mode optical fibers and single-modeoptical fibers with etched cladding so as to couple the core andcladding modes of those optical fibers. These configurations are usefulin realizing two-port optical devices such as a band stop filter ordynamic equalizing filter. In this application light is coupled betweenthe fundamental mode of the optical waveguide and a higher order modethat is subsequently lost.

FIG. 8 depicts an alternative embodiment of the optical signal processor14 in the form of an optical signal processor 70, in which the contactportions 32 of the positioning elements 20 are fixed to the adjacentoptical waveguide 12 by a suitable means such as fusing, or an adhesivethat is compatible with the optical waveguide 12. Because the contactportions 32 are fixed to the optical waveguide 12, each positioningelement 20 can both push and pull the optical waveguide 12, therebynegating any need for a second set of contact portions 32 located on theother side of the optical waveguide 12, and halving the number ofcontact portions 32 for a given application. Each positioning element 20can be deflected in a desired direction so as to push or pull theoptical waveguide 12, by setting the polarity of the voltage across thepositioning element 20 to induce bending of the positioning element 20in the desired direction.

FIG. 9 depicts another alternative embodiment in the form of an opticalsignal processor 74. The optical signal processor 74 is substantiallythe same as the optical signal processor 70, with the exception that thecontact portions 32 of the positioning elements 20 are separated fromthe optical waveguide 12 by an auxiliary member 76. This configurationcan be used, for example, where the index of refraction of the opticalwaveguide 12 is relatively low, and fixing the optical waveguide 12directly to the contact portions 32 of the positioning elements 20 wouldresult in a relatively high loss of optical power. Instead, the contactportions 32 can be fixed to the auxiliary member 76, which can be formedfrom a material having a sufficiently low index of refraction to preventthe optical modes propagating in the optical waveguide 12 frompenetrating into the auxiliary member 76. Because the auxiliary member76 has a lower index of refraction than the optical waveguide 12,contact between the optical waveguide 12 and the auxiliary member 76will not result in power losses in the optical signal that couldotherwise occur due to contact between the optical waveguide 12 and amaterial having a higher index of refraction.

FIGS. 10 and 11 depict another alternative embodiment in the form of anoptical signal processor 200 comprising an optical waveguide 12, and anactuator system comprising a plurality of positioning elements 202. Onlyone of the positioning elements 202 is depicted in FIGS. 10 and 11, forclarity of illustration.

Each positioning element 202 is disposed in a substantially horizontalorientation, as shown in FIG. 10. The positioning elements 202 can eachinclude a 31-mode piezoelectric actuator 204, i.e., a piezoelectricactuator comprising a layer of piezoelectric material having a d₃₁piezoelectric coefficient, sandwiched between first and second layers ofmetallic material that act as electrodes when the positioning element202 is energized. The first and second layers can be electricallyconnected to opposite poles of the voltage source 38.

Each positioning element 202 also includes a contact portion such as thecontact portion 32 described above in relation to the positioningelements 20. A lower end of the contact portion 32 can be securelyembedded in the associated piezoelectric actuator 204 proximate a firstend thereof, by a suitable means such as an interference fit oradhesive. A second end of the piezoelectric actuator 204 can be fixed inrelation to the optical waveguide 12.

Each piezoelectric actuator 204, when subjected to a potential from thevoltage source 38, contracts or expands along its longitudinal axis inan amount proportional to the potential, as denoted by the arrows 214 inFIGS. 10 and 11. Movement of the piezoelectric actuator 204 causes thecontact portion 32 of the positioning element 202 to contact theadjacent portion of the optical waveguide 12, and to pull the adjacentportion in the direction in which the piezoelectric actuator 204 ismoving, as denoted by the arrows 214. Microbends can be imposed on theoptical waveguide 12 by pulling localized portions of the opticalwaveguide 12 in opposite directions using the positioning elements 202.The controller 40 can be configured to control the voltage supplied tothe piezoelectric actuator 204 of each positioning element 202 so as toimpose a series of microbends in the optical waveguide 12 which resultin a desired spectral response in the switch 200, as discussed above inrelation to the optical signal processor 14.

FIGS. 12 and 13 depict a variant of the optical signal processor 200 inthe form of an optical signal processor 230 comprising an opticalwaveguide 12, and an actuator system comprising a plurality ofpositioning elements 232. Only one of the positioning elements 232 isdepicted in FIGS. 12 and 13, for clarity of illustration.

Each positioning element 232 can include a piezoelectric actuator suchas the piezoelectric actuator 204 of the optical signal processor 200,and an enclosure 236 within which the piezoelectric actuator 204 ismounted. The enclosure 236 has six sides or facets. The facets areformed from a rigid or semi-rigid material, and are joined to each otherin a manner that permits the facets to pivot in relation to each other.Each positioning element 232 can further include a carrier 238, and acontact portion 32 mounted in the carrier 238 by a suitable means suchas an interference fit or adhesive.

The carrier 238 is fixed to two of the facets, designated 237 a, 237 b,that extend substantially in the vertical direction, by a suitable meanssuch as a pin or other type of fastener. The other two facets thatextend substantially in the vertical direction, designated 237 c, 237 d,are fixed to a static support by a suitable means such as a pin or othertype of fastener.

Opposite ends of the piezoelectric actuator 204 can be fixed to thehorizontally-oriented facets, i.e., the top and bottom facets,designated 237 e, 237 f, so that the piezoelectric actuator 204 has asubstantially vertical orientation. Contraction of the piezoelectricactuator 204 in response to being energized by the voltage source 38pulls the facets 237 e, 237 f toward each other, as denoted by thearrows 239 in FIGS. 12 and 13. Movement of the facets 237 e, 237 ftoward each other pushes the facets 237 a, 237 b outwardly, as denotedby the arrows 239, which in turn pushes the contacting element 32 andthe adjacent portion of the optical waveguide 12 outwardly. Thegeometric configuration of the enclosure 236 amplifies the movement ofthe piezoelectric actuator 204, so that the carrier 238 and theassociated contact portion 32 move outwardly by a distance that isgreater than the distance by which the piezoelectric actuator 204contracts. It should be noted other means for achieving displacementamplification can be used in alternative embodiments, such as class 1 orclass 3 levers, hydraulics, pneumatics, inclined planes, screws, etc.

FIGS. 14 and 15 depict a variant of the optical signal processors 200,230 in the form of an optical signal processor 250 comprising an opticalwaveguide 12 and an actuator system comprising a plurality ofpositioning elements 252. Only one of the positioning elements 252 isdepicted in FIGS. 14 and 15, for clarity of illustration.

Each positioning element 252 can include a piezoelectric actuator suchas the piezoelectric actuator 204, a substantially C-shaped clip 254, acarrier 238, and a contact portion 32 are mounted in the carrier 238 bya suitable means such as an interference fit or adhesive. End portions256 a, 256 b of the clip 254 can be fixed to the piezoelectric actuator204 by a suitable means such as adhesive or fasteners. A middle portion256 c of the clip 254 can be fixed to the carrier 238 by a suitablemeans such as a pin or other type of fastener. One end of thepiezoelectric actuator 204 can be fixed in relation to the opticalwaveguide 12.

Contraction of the piezoelectric actuator 204 in response to beingenergized by the voltage source 38 pulls the end portions 256 a, 256 bof the clip 254 toward each other, as denoted by the arrows 258 in FIGS.14 and 15. Movement of the end portions 256 a, 256 b toward each otherpushes the middle portion 256 c outwardly, in the direction denoted bythe arrows 258, which in turn pushes the contacting element 32 and theadjacent portion of the optical waveguide 12 outwardly. The geometricconfiguration of the clip 254 amplifies the movement of thepiezoelectric actuator 204, so that the carrier 238 and the contactportion 32 move outwardly by a distance that is greater than thedistance by which the piezoelectric actuator 204 contracts.

FIGS. 16 and 17 depict another variant of the optical signal processor200 in the form of an optical signal processor 270 comprising an opticalwaveguide 12, and an actuator system comprising a plurality ofpositioning elements 272. Only one of the positioning elements 272 isdepicted in FIGS. 16 and 17, for clarity of illustration.

Each positioning element 272 can include a piezoelectric actuator 278,and two contact portions 280. The piezoelectric actuators 278 and thecontact portions 280 are substantially the same as the respectivepiezoelectric actuators 204 and contact portions 32 of the opticalsignal processor 200, with the exceptions noted below.

One end of the piezoelectric actuator 278 is fixed, and other end isunrestrained as depicted in FIGS. 16 and 17. Both of the contactportions 280 of each positioning element 272 are elongated, and extendthrough a single rectangular hole 282 formed in the piezoelectricactuator 278. An end of each contact portion 280 is fixed to a locationbelow its associated piezoelectric actuator 278, and the other end ofthe contact portion 280 is unrestrained, as shown in FIG. 16. Thepiezoelectric actuator 278, when subjected to a potential from thevoltage source 38, contracts or expands along its longitudinal axis inan amount proportional to the potential, as denoted by the arrows 284 inFIGS. 16 and 17. Movement of the piezoelectric actuator 278 in onedirection causes one of the contact portions 280 to pull the adjacentportion of the optical waveguide 12 in that direction. Movement of thepiezoelectric actuator 278 in the opposite direction causes the othercontact portion 280 to pull the adjacent portion of the opticalwaveguide 12 in the opposite direction.

FIGS. 18 and 19 depict another variant of the optical signal processor200 in the form of an optical signal processor 290 comprising an opticalwaveguide 12, and an actuator system comprising a plurality ofpositioning elements 292. Only one of the positioning elements 292 isdepicted in FIGS. 18 and 19, for clarity of illustration.

Each positioning element 292 can include a piezoelectric actuator 298, acarrier 238, and a contact portion 32 mounted in the carrier 238 by asuitable means such as an interference fit or adhesive. An end of thecarrier 238 can be fixed to the outwardly-facing electrode of theassociated piezoelectric actuator 298 as shown in FIGS. 18 and 19, by asuitable means such as adhesive.

The piezoelectric actuators 298 are 33-mode piezoelectric actuators,i.e., each piezoelectric actuator 298 comprises a layer of piezoelectricmaterial having a d₃₃ piezoelectric coefficient. Because thepiezoelectric actuators 298 are 33-mode piezoelectric actuators, thepiezoelectric actuators 298 contract in a direction parallel to thedirection of the voltage applied thereto. Thus, the piezoelectricactuators 298 are oriented vertically as shown in FIG. 18, so that thecontraction thereof pulls the carrier 238 and the adjacent portion ofthe optical waveguide 12 inwardly, as denoted by the arrows 299 in FIGS.18 and 19.

FIGS. 20 and 21 depict another variant of the optical signal processor200 in the form of a optical signal processor 310 comprising a opticalwaveguide 12, and an actuator system comprising a plurality ofpositioning elements 312. Only one of the positioning elements 312 isdepicted in FIGS. 20 and 21, for clarity of illustration.

Each positioning element 312 can include a piezoelectric actuator 318,and a contact portion 32. A bottom of the positioning element 312 can befixed in relation to the optical waveguide 12 as shown in FIG. 20, by asuitable means such as adhesive.

The piezoelectric actuators 318 are 15-mode piezoelectric actuators,i.e., each piezoelectric actuator 318 comprises a layer of piezoelectricmaterial having a d₁₅ piezoelectric coefficient. Because thepiezoelectric actuators 318 are 15-mode piezoelectric actuators, thepiezoelectric actuators 318 experience a shear strain when subjected toa potential. This shear strain causes the top portion of eachpiezoelectric actuator 318, the associated contact portion 32, and theadjacent portion of the optical waveguide 12 to deflect in asubstantially horizontal direction, as denoted by the arrows 320 and asdepicted in phantom in FIGS. 20 and 21.

FIGS. 22 and 23 depict another variant of the optical signal processor200 in the form of a optical signal processor 330 comprising an opticalwaveguide 12, and an actuator system comprising a plurality ofpositioning elements 332. Only one of the positioning elements 332 isdepicted in FIGS. 22 and 23, for clarity of illustration.

Each positioning element 332 can include an electrostatic relay 338, acarrier 238, and a contact portion 32 mounted in the carrier 238 by asuitable means such as an interference fit or adhesive.

A positive pole 340 of each electrostatic relay 338 can be fixed inrelation to the optical waveguide 12, as shown in FIGS. 22 and 23. Anegative pole 342 of the relay 238 can be fixed to the associatedcarrier 238 by a suitable means such as adhesive, and can be biased awayfrom the positive pole 340 by a spring 344.

The poles 340, 342 of the relay 238 can be electrically connected to thevoltage source 38. The negative pole 342 of the relay 338 deflectsinwardly against its spring bias and toward the positive pole 340, asdenoted by the arrows 346 in FIGS. 22 and 23, in response to theelectric field generated when the relay 338 is energized. The inwardmovement of the negative pole 342 moves the associated carrier 238,contact portion 32, and adjacent portion of the optical waveguide 12inwardly in a corresponding manner.

We claim:
 1. A method for altering spectral characteristics of anoptical signal being transmitted through a waveguide, comprising:providing an actuator mechanism comprising at least one positioningelement operable to deflect the waveguide; disposing the waveguidebetween two contact portions of the at least one positioning elementwhich are fixedly coupled to a single elongate piezoelectric actuator;and imposing one or more static deflections on the waveguide using theat least one positioning element by causing a free end of the singleelongate piezoelectric actuator to bend in a first directionperpendicular to a longitudinal axis of the single elongatepiezoelectric actuator when a first electric field is applied theretoand bend in a second direction opposed to the first direction when asecond electric field is applied thereto.
 2. The method of claim 1,wherein imposing one or more static deflections on the waveguide usingthe one or more positioning elements comprises imposing one or morestatic bends in the waveguide using the one or more positioningelements.
 3. The method of claim 1, wherein imposing one or more staticbends in the waveguide using the one or more positioning elementscomprises imposing one or more static bends in the waveguide so as tocouple propagation modes within the waveguide.
 4. The method of claim 3,wherein imposing one or more static bends in the waveguide using the oneor more positioning elements comprises imposing at least two staticbends of different amplitudes in the waveguide.
 5. The method of claim1, wherein imposing one or more static deflections on the waveguideusing the one or more positioning elements comprises deflecting at leastone portion of the waveguide in a direction substantially perpendicularto a longitudinal axis of the waveguide.